A web tag is any user-generated word or phrase that can be associated with web content. Tagging helps organize web content and label it in a way that has personal meaning to the tagging user. Allowing users to tag items with self-chosen labels can result in better or stronger identification of the content. Tagging allows multiple people to opine, in public, what they think about particular pages or images. Tag clouds (or word clouds) are lists or visual displays of tags weighted by popularity. For example, tag clouds can be graphical representations of popular tags pertaining to a web site or web page with attributes such as popularity or importance of individual tags being indicated by font size or color of tags. Examples of websites that use tags or tag clouds include technorati.com, delicious.com, flicr.com, last.fm, and librarything.com
Tagging is seen as a useful aspect enabling systems such as social networking or web 2.0 based systems. By enabling a tagging mechanism for resources like web pages, interesting applications can be built using the resource's tag set. For example, search applications, rating systems and enterprise-wide expertise builder systems can be built using the tags that might come in from various tagging repositories. However, relying on tag sets in building applications and systems is not free of risk. If agents or bots are written to maliciously sabotage tagging systems by introducing tags that pollute the tag set, then systems that depend on the tag set could produce wrong or incoherent results.
As social networking systems or systems that utilize tagging become more popular, it is likely that hackers will create more mechanisms to will attempt to sabotage these systems.